Male and Female Aggression: Lessons from Sex, Rank, Age, and Injury in Olive Baboons

Behavioral Ecology doi:10.1093/beheco/ars021 Advance Access publication 13 March 2012 Original Article Male and female aggression: lessons from sex, rank, age, and injury in olive baboons a,b b,c d e b Holly A. MacCormick, Daniel R. MacNulty, Anna L. Bosacker, Clarence Lehman, Andrea Bailey, Downloaded from D. Anthony Collins,f and Craig Packerb aDepartment of Ecology and Evolutionary Biology, Center for Ocean Health, University of California, 100 Shaffer Road, Santa Cruz, CA 95060, USA, bDepartment of Ecology, Evolution, and Behavior, University of Minnesota, 1987 Upper Buford Circle, St Paul, MN 55108, USA, cDepartment of Wildland Resources, d Utah State University, 5230 Old Main Hill, Logan, UT 84322, USA, Department of Biology, Carleton http://beheco.oxfordjournals.org/ College, 1 North College Street, Northfield, MN 55057, USA, eCollege of Biological Sciences, 123 Snyder Hall, 1474 Gortner Avenue, Saint Paul, MN 55108, USA, and fGombe Stream Research Center, PO Box 185, Kigoma, Tanzania Aggression is ubiquitous, influencing reproduction through inter- and intraspecific effects in ways that reflect life-history strategies of species. In many social mammals, females remain in their natal group for life, whereas males emigrate and compete for rank in other social groups. Competition for rank is inherently risky. Therefore, it has long been hypothesized that risks of injury depend on an individual’s sex, rank, and age in ways that maximize an individual’s reproductive output. However, studies quantifying such risks have been lacking. We analyzed 20 years of long-term data on wounds among olive baboons (Papio anubis) at Materials Acquisitions Dept., University Libraries on May 25, 2012 in Gombe National Park, Tanzania. Males received significantly more wounds than female baboons, and both sexes received the most wounds at ages when they competed most intensely for rank. Immature females received more wounds than immature males in their natal groups, and immature females were more likely to be wounded by females than were immature males. Males in their natal group were wounded less often than immigrant males of the same age. The risk of wounding did not depend on rank in females but rose with rank in immigrant males. Lastly, females received significantly more wounds when cycling (not pregnant or lactating). This study is among the first to quantify the risk of injury for competitors of different sexes, ages, and ranks in social groups. Our results support the prediction that individuals target aggression toward present and future competitors and suggest that sexual coercion increases the risk of wounding in cycling females. Key words: competition, injury, life history, olive baboon, Papio anubis, rank. [Behav Ecol 23:684–691 (2012)] INTRODUCTION for life (i.e., ‘‘female philopatry’’), whereas males immigrate into preexisting groups at puberty (i.e., ‘‘male-biased natal ompetition and sex are inextricably linked. This linkage dispersal’’) (Packer 1979a; Greenwood 1980; Dobson 1982; broadly spans taxa and affects the very structure and C Waser and Jones 1983). evolutionary dynamics of species. In social species, the relation- In many female-philopatric species, female rank is largely de- ship between competition and sex depends on such factors as termined by birth order and maternal rank (Kawamura 1958; reproductive strategies of the sexes, age and social rank of indi- Koford 1963; Koyama 1967; Cheney 1977; Holekamp and Smale viduals, and the life history of the species. Studies of related 1991). In contrast, male rank rises or falls according to the phenomena include primates (Clutton-Brock and Harvey outcome of pairwise interactions between males that reflect 1977; Muller and Wrangham 2009), birds (Wiley 1974; Arcese the competitor’s body size and physical condition (Hausfater 1989), rodents (Dobson 1982; Edelman 2011), carnivores 1975; Packer 1979b; van Noordwijk and van Schaik 1988; Haley (Bekoff et al. 1984), ungulates (Andersen et al. 2000), insects et al. 1994; Pelletier and Festa-Bianchet 2006). High-ranking (Kemp and Alcock 2003), and arachnids (Ulbrich and Henschel males have preferential access to females in many social mam- 1999). However, comparatively few studies have directly quanti- malian species with dominance hierarchies (e.g., LeBoeuf 1974; fied the risks of competition by linking competition with the Clutton-Brock et al. 1982; Moore et al. 1995; Constable et al. incidence of physical wounding. Social mammals, specifically 2001; Alberts et al. 2003; Natoli et al. 2007; Altmann et al. 2010). primates, provide an excellent system to explore this question However, individuals in their natal group often show reduced because of differences between the sexes that apply to many sexual attraction toward close kin (Packer 1979a; Pusey 1980; social mammalian species; females remain in their natal group Bolhuis et al. 1988; Simmons 1991; Manson and Perry 1993; Sterck et al. 2005). Thus, males typically do not engage in intra- Address correspondence to H.A. MacCormick. E-mail: maccormick@ sexual competition for females until dispersing to new groups biology.ucsc.edu. (Packer 1979a; Pusey and Packer 1987). As physical condition Received 9 February 2011; revised 25 August 2011; accepted 26 declines with age, older male baboons rely less on direct con- November 2011. frontation with high-ranking peers to obtain mating opportuni- ties and instead adopt alternative strategies such as forming Ó The Author 2012. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved. For permissions, please e-mail: [email protected] MacCormick et al. • The effect of age, sex, and rank on the risk of injury in olive baboons 685 coalitions with other subordinate males and cultivating relation- METHODS ships with individual females (DeVore 1965; Packer 1977; Smuts Study area and population 1985; Bercovitch 1986, 1988; Noe¨ and Sluijter 1990; Alberts et al. 2003). Thus, direct aggressive competition is often most Gombe National Park, Tanzania, is comprised of a chain of intense between young, high-ranking immigrant males (Packer steep valleys flanked by Lake Tanganyika to the west and a rift 1979b; Yoccoz et al. 2002; Mainguy and Coˆte 2008). escarpment to the east (van Lawick-Goodall 1968; Packer Competition among females generally involves access to 1979a). A total of 671 male and 471 female baboons from resources rather than mates (Trivers 1972). Female per capita 12 different groups (hereafter ‘‘troops’’) have been studied reproductive success often declines with increasing group size since 1967; demographic data have been recorded daily since (van Noordwijk and van Schaik 1999 [macaques]; Packer et al. 1972 (Packer et al. 1998). 2000 [olive baboons]; Altmann and Alberts 2003 [Papio spp.]). Thus, infant females often represent future competi- Wounding and dominance data Downloaded from tion for adult females, whereas infant males will eventually disperse to compete elsewhere. Therefore, adult females are Data on wounding and dominance rank are available from expected to employ behaviors that limit the survival of unre- January 1983 to November 2001. Tanzanian field assistants col- lated juvenile females, though documented examples of adult lected all data under the supervision of D.A.C. with assistance females selectively harassing immature females remain rare from A.B. ‘‘Wounds’’are defined as gashes, cuts, or punctures of (for toque [Macaca s. sinica] and bonnet [Macaca radiata] the skin. Monthly reports provide details on the date and num- macaques, e.g., Dittus 1979; Silk et al. 1981). ber of wounds for each baboon and indicate the cause of http://beheco.oxfordjournals.org/ Studies of intersexual aggression suggest that males are the wounding when witnessed (93 of 2078 cases of wounding). predominant aggressor and disproportionately wound females In addition to monthly reports, daily demographic records also (Muller and Wrangham 2009). Smuts (1985) found that female note the number of fresh wounds. Analyses where the sex of the olive baboons were the targets of male aggression approxi- attacker is known, and those assessing sexual coercion, are done mately once every 17 h. Adult male olive baboons are formida- separately for the number of wounding events and the number ble opponents, and males are approximately twice as large as of wounds received in a year. ‘‘Wounding events’’ are defined as females and have canines about a third longer and wider than the occurrence of one or more wounds on a single day. A dis- females (Virgadamo et al. 1972). Male olive baboons are also tinction is drawn between annual wounding events and the an- formidable relative to other animals. Male baboons have canine nual number of wounds because the likelihood of receiving teeth whose relative size can exceed those of felids, and pri- a wounding event versus several wounds at once may vary for mates in general can have canine teeth that are as long as individuals of different sexes, ages, and ranks. An individual at Materials Acquisitions Dept., University Libraries on May 25, 2012 carnivores, relative to their body size (Lucas 1982; Plavcan may receive many wounds in a single aggressive encounter or and Ruff 2008). Females may be at greater risk of wounding may receive few wounds in multiple aggressive encounters over during particular times if their reproductive state (e.g., cycling, the course of several different days. In all other analyses, wound- consorting with males, etc.) alters

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